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This is not a joke, I am really asking: how do you measure the accuracy of an air quality monitor? Comparing it to another monitor? Creating an air pollution co

This is not a joke, I am really asking: how do you measure the accuracy of an air quality monitor? Comparing it to another monitor? Creating an air pollution condition and seeing how close to that is the measurement?

crazygringo 3y ago
You don't really need super accuracy in the way you do for a body weight scale where a 2% change matters. You watch the readings go up and down as you close windows and cook and then open windows and let the fresh air in. You'll watch CO2 go up to 1200 and then back down to 500. Or PM2.5 go from 2 to 25 and back. They're big changes that obviously correlate in logical ways with what is happening in your home. And then it's really the relative changes you're watching. Even if values are off by 20% it doesn't really matter a ton for private personal use. Because you're really just learning what the baseline values are for fresh air, how quickly values grow, and therefore when you prefer to open some windows. (Or this week, close them.)
baq 3y ago
Generalized, this is unsurprisingly a field of science: https://en.m.wikipedia.org/wiki/Metrology https://en.m.wikipedia.org/wiki/Metrology
Rebelgecko 3y ago
The state of the art for reasonably priced CO2 monitors seems to be that they hard code in the "ambient" Co2 level and instructions tell you to let it sit outside every once in a while. The the sensor adjusts can adjust it's baseline accordingly , assuming that the lowest CO2 level it's seen in the last week or so is equivalent to the "ambient" outside level. Ofc this is susceptible to issues and can require even more adjustments since CO2 levels go up every year. A sensor from 10 years ago might read 5% lower than a modern one because it's using an out of date baseline CO2.
- adhesive_wombat 3y ago
  New shareholder value opportunity: Pay an extra 10% and get a dynamic baseline model that hardcodes a baseline level and expected gradient of 0.5% per year. By the time the device lands in landfill, it probably won't ever have been too far off. And if the CO2 curve derivative starts to underperform and risk your deployed calibrations, throw some dollars an some anti-nuclear campaigns as that's cheaper than doing an update!
- EVa5I7bHFq9mnYK 3y ago
  Here we are talking about 1-2 ppm accuracies. I don't need more than 100ppm accuracy from my CO2 monitor. Hell, just show me one of 4 values: 400, 600, 800 and 1000+ but don't lie.
  - electroly 3y ago
    The second part of OP's post maybe, but not the first part about needing to place the device outside to set the ambient baseline. They basically can't measure at all without that. My Aranet4 was more like 1000 ppm off before putting it outside for awhile, despite being labeled as calibrated from the factory. It was going absolutely ballistic thinking my apartment was full of smog. After sitting outside to get a taste of ambient air, suddenly the inside of my apartment was fine.
- nicbou 3y ago
  That last sentence was a punch in the gut
Leo_Germond 3y ago
One way is to set up a flottila of sensors around a certified control sensor, such as an aerotrack, and measure how they evolve in regards to age, temperature, wind, level of pollutants, ans measurement time. That is a pretty rich task, because low cost sensors will vary wildly in performance due to mechanical variations.

crazygringo 3y ago

You don't really need super accuracy in the way you do for a body weight scale where a 2% change matters. You watch the readings go up and down as you close windows and cook and then open windows and let the fresh air in. You'll watch CO2 go up to 1200 and then back down to 500. Or PM2.5 go from 2 to 25 and back. They're big changes that obviously correlate in logical ways with what is happening in your home. And then it's really the relative changes you're watching. Even if values are off by 20% it doesn't really matter a ton for private personal use. Because you're really just learning what the baseline values are for fresh air, how quickly values grow, and therefore when you prefer to open some windows. (Or this week, close them.)

baq 3y ago

Generalized, this is unsurprisingly a field of science: https://en.m.wikipedia.org/wiki/Metrology https://en.m.wikipedia.org/wiki/Metrology

Rebelgecko 3y ago

The state of the art for reasonably priced CO2 monitors seems to be that they hard code in the "ambient" Co2 level and instructions tell you to let it sit outside every once in a while. The the sensor adjusts can adjust it's baseline accordingly , assuming that the lowest CO2 level it's seen in the last week or so is equivalent to the "ambient" outside level. Ofc this is susceptible to issues and can require even more adjustments since CO2 levels go up every year. A sensor from 10 years ago might read 5% lower than a modern one because it's using an out of date baseline CO2.

adhesive_wombat 3y ago
New shareholder value opportunity: Pay an extra 10% and get a dynamic baseline model that hardcodes a baseline level and expected gradient of 0.5% per year. By the time the device lands in landfill, it probably won't ever have been too far off. And if the CO2 curve derivative starts to underperform and risk your deployed calibrations, throw some dollars an some anti-nuclear campaigns as that's cheaper than doing an update!
EVa5I7bHFq9mnYK 3y ago
Here we are talking about 1-2 ppm accuracies. I don't need more than 100ppm accuracy from my CO2 monitor. Hell, just show me one of 4 values: 400, 600, 800 and 1000+ but don't lie.
- electroly 3y ago
  The second part of OP's post maybe, but not the first part about needing to place the device outside to set the ambient baseline. They basically can't measure at all without that. My Aranet4 was more like 1000 ppm off before putting it outside for awhile, despite being labeled as calibrated from the factory. It was going absolutely ballistic thinking my apartment was full of smog. After sitting outside to get a taste of ambient air, suddenly the inside of my apartment was fine.
nicbou 3y ago
That last sentence was a punch in the gut

Leo_Germond 3y ago

One way is to set up a flottila of sensors around a certified control sensor, such as an aerotrack, and measure how they evolve in regards to age, temperature, wind, level of pollutants, ans measurement time. That is a pretty rich task, because low cost sensors will vary wildly in performance due to mechanical variations.